A known example of using a composite oxide having a tungsten-bronze structure (hereinafter referred to as “tungsten-bronze-type composite oxide”) is as a piezoelectric ceramic for an actuator disclosed in Patent Document 1. This piezoelectric ceramic for an actuator is mainly composed of crystal grains of a tungsten-bronze-type composite oxide represented by a general formula NaSr2Nb5O15 in which a part of Nb is substituted with V and/or Ta. By substituting a part of Nb with V and/or Ta, the Curie temperature Tc is increased to 150° C. or higher, and at least one of the relative dielectric constant and the electromechanical coefficient (d33) are improved.
These piezoelectric characteristics are further improved by substituting a part of Sr in the general formula with an alkaline earth A (at least one element of Mg, Ca and Ba), and in addition, substituting a part of Na with K. Furthermore, Mn and Cu are added as an auxiliary component in an amount in the range of 0.1 to 1.5 weight percent in terms of oxides thereof, thereby improving the sinterability of the piezoelectric ceramic.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-240759